Search Results (47)

Hyporheic zone exchange processes are strongly influenced by channel morphology, producing heat transfer patterns with distinct vertical stratification. To evaluate the effects of different channel geomorphic units on hyporheic temperature dynamics, monitoring sites were established along a segment of the Xiajiasi River (Hubei Province, China) encompassing four representative channel types: a meandering reach, a pool–riffle reach, a weir reach, and a straight reach. Hyporheic temperatures were recorded at multiple depths (0, 0.1, 0.2, and 0.3 m) during both summer and winter. The results indicate that channel morphology strongly controls the spatiotemporal distribution of hyporheic temperatures. Across all channel types, sediment temperatures exhibited depth-dependent amplitude attenuation and phase lag, with mean temperatures decreasing with depth in summer and increasing with depth in winter. The meandering reach exhibited the highest summer temperatures (28.3–30.6 °C), whereas the pool–riffle reach displayed the steepest thermal gradients (deep sediment temperatures as low as 25.6 °C). In contrast, the straight reach exhibited the weakest thermal buffering capacity. The presence of the weir markedly modified downstream thermal conditions, reducing sediment temperatures by approximately 1.6–3.2 °C during summer, whereas overall winter observations demonstrated a pronounced thermal inversion with deep sediment temperatures increasing by 1.2–2.9 °C. These findings demonstrate that distinct geomorphic units create diverse thermal niches; river managers can incorporate diverse geomorphic features into river restoration designs to create localized thermal refugia, thereby protecting temperature-sensitive aquatic species. Full article

The hyporheic zone (HZ) mediates biogeochemical exchanges between rivers and aquifers, yet its spatial and temporal dynamics in large, regulated rivers remain poorly characterized due to limitations of point-based measurements. Here, we combined three time-lapse electrical resistivity tomography (T-ERT) surveys with continuous hydrological and hydrochemical monitoring along a meandering reach of the lower Yellow River, generating a two-dimensional, profile-integrated view of HZ geometry under three hydrodynamic states: low flow (1 December 2020), natural rising stage (1 March 2021), and peak stage during the Xiaolangdi (XLD) water-and-sediment regulation (1 July 2021). Absolute tomograms identified two hydrostratigraphic units: an upper sandy-silt cap (35–170 Ω·m) and an underlying sand aquifer (12–35 Ω·m). Percent-difference tomograms, relative to the low-flow baseline, revealed lateral HZ expansion from ~15 m and vertical growth of 2.5 m at the rising stage to ~36 m and 4.5 m at peak stage, with local resistivity decreases exceeding 38%. In contrast, the deeper mixing zone varied by <10% across surveys. Temperature, rainfall infiltration, and groundwater freshening could not explain the observed patterns. These results were corroborated by three independent lines of evidence: lateral conductivity excursions and in-well temperature records at floodplain well W2, and analytical Darcy–Archie calculations, all consistent with the predicted lateral extent and mixing fraction. River stage, amplified by the XLD release, emerged as the dominant control on two-dimensional HZ geometry. This study provides direct empirical evidence of hyporheic dynamics in a large regulated river and demonstrates that T-ERT, supported by sparse hydrological data, offers a minimally invasive and effective tool for characterizing hyporheic zones. Full article

This study investigates the role of longitudinal aquifer slope in controlling stream–aquifer interaction within bounded floodplain aquifer systems. A series of numerical simulations were conducted to analyze groundwater flow patterns, hyporheic exchange fluxes, and contaminant transport behavior under varying slope conditions. The results showed that increasing slope does not simply enhance hydraulic gradients but fundamentally reorganizes subsurface flow structure. As the slope increases, groundwater flow becomes progressively aligned with the stream, reducing lateral connectivity and confining exchange to a narrow corridor adjacent to the stream. This reorganization leads to the expansion of hydraulically inactive zones and a non-linear response in hyporheic exchange. Exchange flow rates initially increase at low to moderate slopes but decline beyond a threshold at higher slopes, despite higher local gradients. The transition begins at around a 2% slope and becomes pronounced within the range of approximately 3–7%, indicating a shift in flow regime rather than a continuous scaling of interaction intensity. Particle tracking analyses further reveal that slope controls the spatial distribution of contaminant vulnerability. While the overall extent of active transport zones decreases with increasing slope, localized transport potential intensifies near the stream boundary due to higher velocities and reduced residence times. These findings demonstrate that hydraulic gradient magnitude alone is insufficient to characterize stream–aquifer interaction and highlight the importance of flow geometry and connectivity. The results provide a process-based framework for understanding slope-controlled hyporheic exchange and offer insights for improving groundwater vulnerability assessment and management in alluvial systems. Full article

The hyporheic zone functions as a critical interface mediating hydrological and biogeochemical exchanges between stream water and streambed. Within shallow streambed layers, sediment transport and biofilm colonization can induce dynamic layered clogging, alter hydraulic conductivity, and foster physical stratification that significantly modulates hyporheic exchange patterns. This study develops a coupled hydrodynamic–mass transport model for a representative streambed bedform to examine the impacts of biofilm-driven dynamic clogging on hyporheic exchange dynamics. Results reveal that dynamic layered clogging reduces pore water velocity and total water flux, causing a 45.1% decline in the total inflow to the hyporheic zone. The transport of non-absorbable solutes exhibits a biphasic pattern: initial rapid penetration transitions to gradual deceleration over time, with dynamic clogging extending the penetration time of the solute center of mass distribution (CMD). Notably, when hydraulic conductivity falls below a threshold (K* < 0.25), CMD penetration time exhibits a positive correlation with hydraulic conductivity, attributed to porosity-induced changes in actual flow velocity. When considering the anaerobic growth in deeper layers, the penetration time become longer because of the clogging present there. This research clarifies the mechanistic connections between biofilm-induced clogging and hyporheic exchange, providing valuable insights for the management of hyporheic ecosystems and the modeling of biogeochemical processes. Full article

Stream temperatures are expected to increase with warming air temperatures, yet the extent and aquatic health impacts vary significantly across heterogeneous landscapes. This study was conducted in a 3360-ha multi-land-use watershed in the Pacific Northwest region of the USA to assess and compare the driving factors for stream temperature heating, cooling, and cool-water refugia along a 12-km mainstem stream longitudinal profile. Study objectives were to (1) determine yearlong stream temperature variability along the entire stream longitudinal profile, and (2) assess stream-environment relationships influencing stream temperature dynamics across forest, agriculture, and urban landscapes within the watershed. Stream and riparian air temperatures, solar radiation, shade, and related stream-riparian characteristics were measured over six years at 21 stations to determine changes, along the longitudinal profile, of thermal sensitivity, maximum and minimum stream temperatures, and correlation between solar radiation and temperature increases, and potential causal factors associated with these changes. Solar radiation was a primary heating factor for an exposed agricultural land use reach with 57% effective shade, while southern stream aspects and incoming tributary conditions were primary factors for forested reaches with greater than 84% effective shade. Potential primary cooling factors were streambank height, groundwater inflows, and hyporheic exchange in an urban reach with moderate effective shade (79%) and forest riparian width (16 m). Combining watershed-scale analysis with on-site stream-environmental data collection helps assess primary temperature heating factors, such as solar radiation and shade, and potential cooling factors, such as groundwater and cool tributary inflows, as conditions change along the longitudinal profile. Full article

Understanding dynamic groundwater–surface water interactions in alluvial plains is critical for sustainable water resource management, yet seasonal variability and spatial heterogeneity of these exchanges remain imprecisely quantified. Here, we present an improved ²²²Rn mass balance model for evaluating the seasonal hydraulic exchange between groundwater and the Xintongyang Canal in the Taizhou alluvial plain over the course of a hydrologic year. To reduce the model uncertainty, the “background” ²²²Rn for non-groundwater sources was incorporated into the model to replace the influence of hyporheic exchange. The results indicate that the hydraulic exchange process of surface water and groundwater has significant spatiotemporal differences. Based on the calculations from the ²²²Rn mass balance model, the canal leakage flux follows the order of summer > autumn > winter > spring over the course of a hydrologic year. In contrast, the groundwater discharge flux follows the order of summer > spring > autumn > winter. During a hydrological year, summer demonstrated the most intense water exchange dynamics, with peak fluxes reaching 0.0455 m³/(s·m) for surface water leakage and 0.0013 m³/(s·m) for groundwater discharge, revealing pronounced spatial heterogeneity in dominant exchange processes. ²²²Rn activity in canal and groundwater varies significantly across different regions, with canal leakage being the dominant mode of hydraulic exchange within the study area. The change of the hydraulic exchange process was mainly affected by factors such as rainfall. In the process of promoting surface water leakage, precipitation will also strengthen the supplement of groundwater and contribute to the groundwater discharge in most of the canal sections. This study offers insight into the seasonal variations of groundwater and surface water interaction within an alluvial plain. Full article

Negative impacts of human activities on stream ecosystems include the reduction/modification of the connectivity between surface water and groundwater and the contamination of these resources. Vertical hydrological exchanges principally occur through the coarse surface sediments and the hyporheic zone (porous matrix) and these compartments have the property to store pollutants. Such hydrological exchanges participate in the self-purification of the stream and infiltration of polluted surface water can lead to the contamination of groundwater. A complete environmental monitoring program should therefore include the assessment of the biological quality of the porous matrix and of the dynamics of vertical hydrological exchanges. The Functional trait (FTR) method based on the study of oligochaete communities in the coarse surface sediments and the hyporheic zone, allows simultaneous assessment of the effects of pollutants present in these compartments and the dynamics of vertical hydrological exchanges. Here, we applied the FTR method upstream and downstream of the effluents of three different wastewater treatment plants (WWTPs) whose discharges were significantly polluted, and for one of them (Oberglatt), before and after its upgrading. We could clearly observe negative effects of the effluents of each of these WWTPs on oligochaete communities and the Oberglatt WWTP upgrading resulted, compared to the state before the upgrading, in a significant reduction of the polluted sludge effect at the downstream site of the effluent. In addition, the method allowed us to identify several sites where the stream had a high capacity to self-purify (through exfiltration of groundwater) and other sites where groundwater was vulnerable to pollution by surface water. Full article

Water quality is intricately linked to the global water crisis since the availability of safe, clean water is essential for sustaining life and ensuring the well-being of communities worldwide. Pollutants such as industrial chemicals, agricultural runoff, and untreated sewage frequently enter rivers via surface runoff or direct discharges. This study provides an overview of the key mechanisms governing contaminant transport in rivers, with special attention to storage and hyporheic processes. The storage process conceptualizes a ubiquitous reactive boundary between the main channel (mobile zone) and its surrounding slower-flow areas (immobile zone). Research from the last five decades demonstrates the crucial role of storage and hyporheic zones in influencing solute residence time, nutrient cycling, and pollutant degradation. A review of solute transport models highlights significant advancements, including models like the transient storage model (TSM) and multirate mass transport (MRMT) model, which effectively capture complex storage zone dynamics and residence time distributions. However, more widely used models like the classical advection–dispersion equation (ADE) cannot hyporheic exchange, limiting their application in environments with significant storage contributions. Despite these advancements, challenges remain in accurately quantifying the relative contributions of storage zones to solute transport and degradation, especially in smaller streams dominated by hyporheic exchange. Future research should integrate detailed field observations with advanced numerical models to address these gaps and improve water quality predictions across diverse river systems. Full article

The Qinglian River plays a significant role in China’s national water conservation security patterns. To clarify the relationship between hydrogeochemical properties and groundwater quality in this karst-fissure aquifer system, drilling data, hydrochemical parameters, and δ²H and δ¹⁸O values of groundwater were analyzed. Multiple indications (Piper diagram, Gibbs diagram, Na⁺-normalized molar ratio diagram, chloro-alkaline index 1, mineral saturation index, and principal component analysis) were used to identify the primary sources of chemicals in the groundwater. Silicate weathering, oxidation of pyrite and chlorite, cation exchange reactions, and precipitation are the primary sources of dissolved chemicals in the igneous-fissure water. The most relevant parameters in the karst water are possibly from anthropogenic activities, and other chemicals are mostly derived from the dissolution of calcite and dolomite and cation exchange reactions. Notably, the chemical composition of the deep karst water from the karst basin is mainly influenced by the weathering of carbonate and cation exchange reactions and is less affected by human activities. The hydrogeochemical properties of groundwater in the karst hyporheic zone are influenced by the dissolution of carbonates and silicates, evaporation, and the promotion effect of dissolution of anorthite or Ca-containing minerals. Moreover, the smallest slope of the groundwater line from the karst hyporheic zone among all groundwater groups revealed that the mixing effects of evaporation, isotope exchange in water–rock interaction or deep groundwater recharge in the karst hyporheic zone are the strongest. The methods used in this study contribute to an improved understanding of the hydrogeochemical processes that occur in karst-fissure water systems and can be useful in zoning management and decision-making for groundwater resources. Full article

Point bars are crucial elements of river systems, significantly enhancing the nitrogen cycle in riparian zones by facilitating hyporheic exchange between surface water and riparian zones. This study investigated the impact of dissolved oxygen (DO) concentration and temperature on nitrogen transport and reactions in river point bars. A two-dimensional coupled surface water–groundwater model was developed to analyze nitrogen distribution, variations, and reaction rates in rivers with point bars. The model considered three chemical reactions controlling nitrogen transformation: aerobic respiration, nitrification, and denitrification, with DO and temperature as independent variables. The results indicated that DO variations have a limited effect on solute migration depth, whereas increased temperature reduces solute migration depth. At surface water DO concentrations of 0.1, 0.2, and 0.4 mol/m³, nitrate removal in the riparian zone was 0.022, 0.0064, and 0.0019 mol/m, respectively. At riparian temperatures of 5 °C, 15 °C, and 25 °C, nitrate removal was 0.012, 0.041, and 0.16 mol/m, respectively. Nitrogen removal is more sensitive to temperature variations than to changes in DO concentration. In this research, the decrease in DO concentrations and the temperature increase greatly enhanced the riparian zone’s denitrification effect. This study improves our understanding of how riparian zones impact nitrogen cycling under various environmental conditions. Full article

An experimental study was conducted to identify the behaviour of neutrally buoyant microplastics (specific density, 0.94) in different hydrodynamic conditions while focusing on combined wave–current conditions and the mixing across the hyporheic zone. For in-water-column microplastics, it was observed that the streamwise dispersion of neutrally buoyant microplastics is comparable to solute dye in both slow open-channel flow conditions and combined wave–current conditions. However, for in-bed microplastics, when compared to soluble tracers, the longer timespans associated with the hyporheic exchange process allowed the density effects to enhance the vertical exchange when compared to solutes. Full article

Understanding the dynamics of hyporheic flow is important for managing water resources, since this interfacial flow exchange affects the fate and transport of contaminants in rivers. This study numerically quantifies the effect of hyporheic exchange on solute residence times in surface water systems by simulating solute transport in unified turbulent open-channel and hyporheic zone systems. Interfacial hyporheic fluxes (q_int) increase with increased Reynolds number (Re) that produces an enhanced bottom pressure gradient over the ripple bed. Heavy-tailed breakthrough curves emerge when hyporheic flow is considered in transport simulation. This reveals that hyporheic flow is a dominant driver of non-Fickian transport in surface water as this interfacial flow exchange delays solute transport with slow porewater flows. Furthermore, the increase in Re extends the longitudinal spreading of solute tracers because a higher surface flow velocity intensifies the magnitude of hyporheic flow and associated storage effects. This can be confirmed by the ratio of the maximum residence time to the peak arrival time that increases with the increase in Re, following a power-law relationship with both Re and q_int. Full article

The hydrodynamics of a river confluence generate significant vertical, lateral, and stream-wise gradients in the context of velocity, thereby forming a highly complex three-dimensional flow structure, including the development of large-scale turbulence structures. The above features affect the ecologically important underlying hyporheic zone, where surface and subsurface waters interact, and hence affect biological activity and result in highly varied habitats for organisms as well as the whole river environment. The influence of challenging conditions for in situ monitoring of hyporheic exchange—such as non-sinusoidal temperature signals, uncertainty in thermal parameters, and unsteady flows—have led to the development of hyporheic exchange detection methods that are based on the phase and amplitude changes in transient thermal signals. The use of heat as a tracer can require complex steps, including the isolation of the diurnal component of the temperature signal from other signals as well as stochastic variation. The focus of this study was to investigate a field campaign carried out between the Ninemile Creek and its tributary confluence, located in Marcellus, NY. Temperature data of the shallowest saturated sediment layers were measured from April to May 2019. Flux estimations were calculated using VFLUX 2, a MatLab based code, which performed data filtering and DHR (Dynamic Harmonic Regression). The patterns and rates of vertical flux exchange were then analyzed, and sampling of the temporal thermal profiles was performed. Furthermore, multiple analytical solutions of the one-dimensional heat transport model were analyzed and discussed in order to obtain the confluence hydrodynamic effect as well as the variations in the vertical flux estimation. This was achieved by utilizing different sensor pairs and porous medium characteristics, such as thermal diffusivity and conductivity. The predicted flow field shows that confluence topography—which includes the turbulent kinetic energy downstream of the junction, shear layer formations, bed stratigraphy and water table gradients—affects the magnitude and patterns of hyporheic exchange. The results of this study could help to advance the calibration of one-dimensional heat transport models in order to better understand the key hydrological, hydraulic, and ecological issues associated with river confluence. Full article

The hyporheic zone (HZ) is a critical area of all river ecosystems. It is the area beneath the stream and adjacent to the stream, where the surface water and groundwater are mixed. The HZ extends both vertically and laterally depending on the sediment configuration, namely their porosity and permeability. This influences the hyporheic communities’ structural pattern and their active dispersal among distinct rivers compartments and alluvial aquifers. It is still difficult to assess the spatial extent of the HZ and the distribution of the mixing zones. This study applies time-lapse images obtained using electrical resistivity tomography (ERT) of 20 m wide and 5 m deep alluvial streams, with regards to the structural pattern of hyporheic communities represented by cyclopoids and ostracods, in order to assess the extent of the HZ in the riverbed and the parafluvial sediment configurations. The ERT images obtained at the hyporheic Site 1 are characterized by alluvial deposits dominated by coarse and very coarse sands with resistivity values ranging from ~20 to 80 Ohm.m, indicating a permeable zone up to ~0.5 m thick and extending laterally for ca. 5 m from the channel and associated with the hyporheic zone. The sediment configurations, texture, and structure indicate an active surface–hyporheic water exchange and low water retention into the sediments. This is also indicated by the hyporheic copepods and ostracods communities’ structure formed by a mixture of non-stygobites (five species) and stygobites (two species). A low-resistivity (<70 Ohm.m) permeable zone located 2.3 m below the streambed and unconnected with the river channel was also detected and associated with the associated alluvial aquifer. In contrast, the resistivity image at Site 2 dominated by coarse, medium, and very fine sands, shows a low-permeability zone in the upper ~0.5 m of the profile, with a resistivity value ranging from ~45 to 80 Ohm.m, indicating a reduced HZ extension in both vertical and lateral dimensions. Here the sediment configurations indicate that the water retention and interaction with the sediment is higher, reflected by more diverse hyporheic communities and with highly abundant stygobite species. The two examples show that non-invasive ERT images and biological assessments provide complementary and valuable information about the characterization of the sub-channel architecture and its potential hydraulic connection to the floodplain aquifer. Full article

The hyporheic zone (HZ) is important for river ecological restoration as the main zone with nitrogen biochemical processes. The engineering of river ecological restoration can significantly change the hydrodynamics, as well as solute transport and reaction processes, but it is still not fully understood. In this study, nitrogen transport and reaction processes were analyzed in the HZ with an in-stream weir structure. An HZ model was built, and three reactions were considered with different design parameters of the weir structure and different permeability characteristics of porous media. The results show that a structure with a greater height on the overlying surface water enables the species to break through deeper porous media. It promotes the mean spatial reaction rates of nitrification and denitrification and results in increased net denitrification in most cases. In addition, increasing the burial depth of the structure leads to the same variation trends in the mean spatial reaction rates as increasing the structure height. Larger permeability coefficients in porous media can enhance flow exchange and increase mean spatial reaction rates. The results can help deepen the understanding of nitrogen transport and transformation in the HZ and optimize the design parameters and location of the in-stream structure. Full article